Imaging the Structure of the Pacific-North American Plate Boundary using Airborne Laser Swath Mapping (ALSM) Data and Wavelet Analysis
Abstract
Since the 1906 San Francisco earthquake, geologists have noted that the topography of active fault zones is significantly modified by repeated fault ruptures over geologic time. Here, we present an analysis of fault zone topography generated by high-resolution Airborne Laser Swath Mapping (ALSM) data collected by the National Center for Airborne Laser Mapping (NCALM). The digital elevation models (DEMs) generated from the ALSM data reveal the location, orientation, and curvature of scarps associated with active, plate-boundary faults. In particular, we have examined topographic data from the B4 and Northern California data sets, as well as data from faults within the Eastern California Shear Zone. We used a wavelet-based convolution scheme, based on topographic forms modified from the profile scarp-diffusion model of Hanks et al. (1984), extended to encompass along-strike features. We applied this filtering methodology to digital topography along fault zones to estimate the best-fitting height, orientation, morphologic age, and associated Signal-to-Noise Ratio (SNR) of scarps found within these datasets. These results will be available to the community via a GIS web portal so that other workers can mine these data to understand patterns of fault-zone structure observed along the plate-bounding fault zones. To evaluate the utility of this methodology for identifying and characterizing fault scarps within the topographic swaths, we present sample results from the Calaveras fault, part of the San Andreas fault system in northern California. We found that along this fault, the filtering algorithm correctly identifies scarps characterized by ground surveys, previous analysis of aerial photography, and/or field mapping. However, some mapped fault traces with low SNR values because of their subtle morphologic expression are not identified by the algorithm. Similarly, some fluvial scarps that trend in a similar orientation to the overall fault zone are erroneously identified as fault scarps by the algorithm. Future work includes further refinement and field verification of the method, and eventual application to all on-land faults for which ALSM data are available within the western U.S. plate margin.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP41A0576S
- Keywords:
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- 1130 GEOCHRONOLOGY / Geomorphological geochronology;
- 8150 TECTONOPHYSICS / Plate boundary: general;
- 9350 GEOGRAPHIC LOCATION / North America;
- 4319 NATURAL HAZARDS / Spatial modeling